The present application relates to a battery controller, a battery control method, and a program.
A range of voltage applicable to a secondary battery, which can be repeatedly charged and discharged, is defined by an upper voltage and a lower voltage. It is possible to expand the life span of the secondary battery, by setting the applicable voltage range narrower than a range of voltage in which the battery can be charged or discharged. FIG. 7 shows ranges of voltage applicable to secondary batteries for an electric vehicle and for a household, respectively, and voltage ranges in which the secondary batteries for an electric vehicle and for a household can be charged or discharged, respectively.
An upper limit voltage is a set value to or above which the voltage should not be raised when a secondary battery is charged, and is a value which is equal to or lower than a maximum charge voltage. A lower limit voltage is a set value to or below which the voltage should not be lowered when a secondary battery is discharged, and is a value which is equal to or higher than a final discharge voltage.
It is generally known that the degradation of a second battery is accelerated, when the battery is charged at voltage equal to or higher than the maximum charge voltage and, after that, the battery is kept in such state. For this reason, the upper limit voltage of the secondary battery needs to be set to a value which is lower than the maximum charge voltage. Further, when the battery has been discharged at voltage equal to or lower than the final discharge voltage, and when the battery is further discharged, its voltage then rapidly decreases with the discharge. And when the voltage decreases to a certain voltage or less, the corresponding battery cannot be sufficiently charged and would not possibly work. For this reason, the lower limit voltage of the secondary battery needs to be set to a value which is higher than the final discharge voltage.